Device-to-device (D2D) communication means communication directly performed between devices, and is generally classified into D2D unicast communication and D2D broadcast/multicast communication. In a D2D unicast communications system, one device directly communicates only with another device. In a D2D broadcast/multicast communications system, one device sends a data packet of the device to multiple devices near the device.
Regardless of unicast or broadcast/multicast communication, when no base station or controller participates in allocation of D2D communication transmission resources, user equipment selects a D2D communication transmission resource for the user equipment itself. Different user equipment is prone to select a same time-frequency resource to send their respective D2D signals. However, there is mutual interference between these signals, and it is impossible for user equipment to perform both sending and receiving on one time-frequency resource. Therefore, when two devices select a same time-frequency resource to send D2D signals, the two devices cannot receive a D2D signal from each other. In addition, when sending a signal on a sub-band within system bandwidth, user equipment cannot receive a signal from another device on another sub-band within the system bandwidth at the same time. Therefore, when two devices send their respective D2D signals on different sub-bands within the system bandwidth at the same time, the two devices cannot receive a D2D signal from each other.
In conclusion, in D2D communication, because mutual interference is caused when different devices select a same resource to send D2D signals, or a device cannot receive a signal on another frequency band when sending a signal, a receiving failure or faulty receiving is caused in D2D transmission, resulting in low D2D communication reliability.